Method for the identification of the formation fluid invasion moment

ABSTRACT

The method of the formation fluid invasion moment identification consists in the sinking of an apparatus for the sampling of the fluid mixture into the uncased wellbore; the apparatus consists of the body, standard probe, hydraulic system, sample storage chamber and pumping module. Then the fluid mixture is pumped out and simultaneously the temperature of the fluids being pumped out is measured using at least one temperature transducer positioned in the sampling apparatus hydraulic system. Based on the values obtained the graph of the derivative temperature of the pumped out fluids as function of time is built up and the formation fluid invasion moment is identified.

FIELD OF THE DISCLOSURE

The invention is related to a method of identifying a formation fluid invasion and may be used, for example, to determine the filtrate injection depth, formation fluid mobility, viscosity contrast between the formation fluid and filtrate, formation anisotropy value etc.

BACKGROUND OF THE DISCLOSURE

During drilling with a positive differential pressure the drilling mud is injected into the formation and during formation fluid sampling the sample is contaminated. The hydrocarbon sample is contaminated with the oil-based drilling mud. The water sample is contaminated with the water-based drilling mud. Identification of the formation fluid properties using a contaminated sample results in substantial errors. Therefore, to obtain a pure sample a long pumpout process is required during which the sample is cleaned. During the pumpout the formation fluid invasion time identification is very important, for example, for the fluid injection depth identification. The existing methods of the invasion identification are based on measuring the pumped-out fluids' optical density. The disadvantages of the known methods for the formation fluid invasion time identification are measurement errors.

The idea of the sample cleaning process optical monitoring is based on the Beer-Lambert Law stating that the optical density (OD) of the two fluids mixture is equal to the sum of their weighted optical densities with the molar concentrations in the mixture. Obviously, the solution to the equation with two unknown quantities is not the only one and therefore does not provide the identification of the contamination level during the sample purification. To eliminate the solution non-uniqueness an approximated asymptotic solution is introduced.

The closest prior art is the method for the identification of the formation fluid invasion consisting in the sinking of the apparatus for the fluid mixture sampling (containing drilling mud filtrate and formation fluid) into the uncased wellbore, the apparatus consists of the body, standard probe and a hydraulic system described in [[Mullins, O. C., Schroer, J.: Real-time identification of filtrate contamination during openhole wireline sampling by optical spectroscope. Paper SPE 63071 presented at the 2000 SPE Annual Technical Conference and Exhibition, Dallas, Tex., 1-4 Oct. 2000]. The disadvantage of the method above is obtaining an approximate solution for the identification of the formation fluid invasion time.

The proposed method for the identification of the formation fluid invasion time does not require the use of the approximate solution which enables improvement of the formation fluid invasion moment identification.

SUMMARY OF THE DISCLOSURE

The invention is aimed at the facilitation of solving the problem of creating a simple and accurate method of the formation fluid invasion moment identification.

This invention offers a new method of the formation fluid invasion moment identification by temperature measurements providing a more accurate identification of the formation fluid invasion moment.

The method of the formation fluid invasion moment identification comprises the following steps. A sampling apparatus for the formation fluid mixture (consisting of the drilling mud filtrate and formation fluid) is sunk into the uncased wellbore; the apparatus consists of a body, standard probe, hydraulic system, chamber for the sample storage and pumping module; the fluid mixture is pumped out simultaneously with the measurement of the temperature of the fluids being pumped out, the temperature is measured using at least one temperature transducer positioned at the sampling apparatus hydraulic system inlet, by the values obtained the graph of the fluid temperature derivative as function of time is built up, the graph is used to identify the formation fluid invasion moment.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the apparatus for the fluid mixture sampling;

FIG. 2 shows the change of the pumped-out fluids' contamination as function of time and average integral temperature time derivative; and

FIG. 3 shows the change of the sample integral average temperature vs. The pump-out time;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus for the fluid mixture sampling consists of a body 2, at least one temperature transducer 1, a standard probe 3, a pumping module 6, interconnected by a hydraulic system 4 by which, via the standard probe 3 the fluids collected are routed to a sample storage chamber 5. The standard probe may be, in particular, a double-packer one. At least one temperature transducer 1 is mounted at the inlet of the collected fluid sample to the hydraulic system 4.

The method of the formation fluid invasion moment identification is based on the record of the surge of the integral average temperature of the pumped-out fluids. The method is applicable for both vertical and horizontal wellbores.

During the wellbore drilling the temperature profile of the bottom-hole area changes as follows: during the drilling mud circulation the bottom-hole area is cooled down and then during the wellbore shutdown the bottom-hole area temperature is recovered. The temperature of the pumped-out fluids is measured using at least one temperature transducer mounted at the hydraulic system inlet for taking the fluid mixture sample. The fluid mixture consisting of the drilling mud filtrate and formation fluid is pumped out and simultaneously with the pumping-out the temperature of pumped-out fluids is measured using at least one temperature transducer. By the values obtained the graph of the derivative temperature of the pumped-out fluids as a function of time is built up and the formation fluid invasion moment is identified. As FIG. 2 shows, at the moment of the formation fluid invasion the sign of the derivative average integral temperature is changed which corresponds to the occurrence of a small peak at the graph of the derivative temperature of the pumped-out fluids (FIG. 3). By this change record the moment of the formation fluid invasion is identified. 

1. A method for a formation fluid invasion identification comprising the steps of: lowering a fluid mix sampler into an uncased borehole, fluid mix consisting of a drilling mud filtrate and a reservoir fluid, the sampler including an enclosure, a standard probe, a hydraulic system, a chamber for probes storage and a pumping module, pumping off the fluid mix simultaneously with measuring temperature of the fluids being pumped off using at least one temperature transducer located in the hydraulic system of the sampler, constructing a graph of the pumped off fluids temperature derivative as a function of the time based on the values obtained, and determining the formation fluid invasion time.
 2. The method of claim 1 wherein a borehole is vertical.
 3. The method of claim 1 wherein a borehole is horizontal.
 4. The method of claim 1 wherein a standard probe is a double-packer. 